AutoPostBack is a property which is used to postback automatically when an event is raised. You have to set the AutoPostBack property of the control to True.

In the context of ASP.NET or ASP.NET Web Forms, AutoPostBack is a feature that allows a control, such as a TextBox or a DropDownList, to automatically post back to the server when a certain event occurs, typically a user interaction like a change in selection or input.

When AutoPostBack is set to true for a control, any time the control’s value changes or an event associated with it is triggered, such as the SelectedIndexChanged event for a DropDownList, the page is automatically submitted to the server for processing. This allows you to handle user input or selection changes without requiring the user to manually submit the form.

In simpler terms, AutoPostBack eliminates the need for the user to explicitly click a submit button to send data to the server; instead, it triggers a postback event automatically whenever there’s a change in the control’s state. This can be useful for creating more dynamic and responsive web applications.